Improved bridge



tnited @geist-et CHARLES H. PARKER, r OF BOSTON, MASSACHUSETTS.

Letters vPatent N 93,638, dated ngust 10, 1869.

IMPnovnD BRIDGE.

The Schedule referred to in these Letters Patent and making part of the same.

To whom 'it may concer/n.:

Be it known that I, CHAnLns H. PARKER, civil engineer, of Boston, county of Suiolk, and State of Massachusetts, have invented certain new and useful Improvements in Bridges; and I hereby declare'the following to be a full, clear, and exact description ofthe same, reference being had to the'accompanying drawings, in which- Figure 1 is a side` elevation of a bridge embodying ,my invention.

Figures 2, K3,4, and 5 are detailed views of detached parts. Y

The system of bridging, which I claim as my inven- 4tion, is composed of two distinct and separate systems combined, neither one of which, alone, is new.

The foundation or primary system is the cantilever A A, &c., anchored pack' to the shore, either by a. wholly or partially-xell anchorage, or in `continuons spans, each half span serving as au anchorage for its adjacent half of the next span. 'Io providefor the expansion and contraction of the cantilevers, they are left with a free joint at the centre of the span, as shown at o, figs. l, 2, 3'. This joint may be as shown, or in any other mode equivalent.

The design is to proportion' the cantilever so as to carry, with a low factor of safety, the ixedweight of the superstructure, or, 'in other words, the useless load.

This part of the 4system is designed to be distinct and separate from the other part of the combination, the chord of the cantilever being no part of', nor acting as a chord of the other system.

The cantilever' is to bebuilt by projection, and in any ofthe styles or methods lmown'in the simple cantilever bridge, and is, to serve yfor false works during the erection ofthe othersystem.

The secondary system is composed lof a system of independent gird'er, B, supported at bo'th ends, and covering the same clear span as the cantilever or can-v tilevers.v

It can be made with a curved or straight top, of any of the types known, as the bowstring-girder, Warren 'girder, Snc. To provide for contraction br expansion in this secondary system, it ismade free and independent of the primary system, and allowed free movement on rolls, or their equivalent, toward Ithe abutments, pier, or points -of support, asshown in iigs. 4 and 5.

The design is to proportion this secondary system to carry theexternal, rolling, or useful load, with a high factor of safety. Its action is distinct from the primary system.

The weight ofthe whole of the secondary system is carried temporarilyiby the primary system of cantilevers during erection, but after the joining of the arch or toprnember inthe centre, the cantilever isrelieved of the weight of this member, which weight is transferred to the seating of the arch or top-member, on the pier or abutment..

The weight of the tie-chord and the intermediate bracings betweenl the top and bottom-members ofthe secondary system, together with the floor-beams, and all the roadway, is to be Acarried permanently byf'the primary system of cantilevers. y

' The advantages of this system, are, that the complete separation of thel useful, external, 'or rolling load upon the superstructure, and the useless or fixed weight of superstructure, enables meto design the sustaining-power ofthe xed load, with a small factor of safety, while the sustainingpower of the useful or external rolling load, being separated from and no part of the part carrying the xed load, can be designed with a high factor of safety.

Thus the strains occasioned by the two, can be dealt with separately and more economically.

It also enables me to construct the sustaining-power of the superstructure of metal, and the sustainingpower of the useful or rolling load temporarily ot wood, with a view to save rst cost and to eventually replace the woodeby iron, without disturbing the primary system, which supports the weight of the super- Y structure; and, furthermore, in metallic structures,

each system takes care of its own expansion and contraction, independent ofand without affecting the other.

What I claim as new, and desire to secure by Letters Patent, is-

The combination of two distinct systems of bridg-A ing, composed of a cantilever or cantilevei's, with a wholly or partially-fixed anchorage, free to expand at its unsupported, end or centre of a span, where two meet, with a system of independent grder, supported at both ends and covering the same' clear span as the cantilever, and free to expand toward the abutments or points of support, the chord o r chords of one'system' being distinct and separate from the chord or chords of the other, substantially as herein shown and set forth. In testimony whereof, 1 have signed my name to this specification, before two subscribing witnesses.

O. H. PARKER.

Witnesses WM. A. BLoDen'r'r,

G.; O unav. 

